It is necessary to install a power cable, a telecommunication cable or other cables, and pipes (cable tubes) through which those cables pass from a vertical zone (vertical direction) to a ceiling zone (horizontal direction) in various buildings such as a factory, a business office, a store, a condominium, a warehouse, a station, a gymnasium and a theater as well as in various structures such as a tunnel, a subway, an elevated railway, an elevated road, and a bridge.
In such a ceiling zone, hanger bolts are mounted to the ceiling at fixed intervals to hold channel rails. Racks are placed on and extend across the channel rails to guidably support cables or cable tubes. The racks are then secured to the channel rails. As an alternative, the cable tubes are directly placed on and extend across the channel rails held by the hanger bolts. The cable tubes are then secured to the channel rails. The channel rail may be directly secured to the ceiling with its opening (slot) being directed downward.
In the vertical zone, the channel rails are secured to structural beams, girders or walls at fixed intervals and extend in a horizontal direction. The racks or cable tubes extend across and are secured to the channel rails.
The channel rail is also referred to as a "hanger rail", "duct channel, or "raceway". In either case, the racks and cable tubes must be secured to each channel rail at points where the racks and cable tubes intersect with each channel rail. A number of securing operations are thus required to complete the installation. A substantial number of securing operations are involved where it is necessary to secure small girders or partitions to the racks, or to secure outlet boxes or other electric devices or components to the channel rails.
To this end, there has been proposed a fixture for securing racks as disclosed in Japanese utility model publication No. 5-19671. The prior art fixture comprises a fixture body having a through opening at a location where the fixture body is attached to a channel rail, a bolt extending through the through opening, and a rectangular slat including a central, internally threaded hole adapted to receive the bolt. The slat has a pair of long sides and a pair of short sides. The long side has a length equal to or greater than the distance between flanges of the channel rail. Diagonally opposite corners of the slat are cut in an oblique fashion. A spring is disposed between the fixture body and the head of the bolt to thereby lift the bolt and the slat.
However, the prior art fixture presents the following problems.
(1) The slat is substantially long and has a length greater than the width of the fixture body. Handling of such a large slat is cumbersome. The orientation of the slat must be adjusted if a change in the orientation of the slat occurs due to contact with hands or articles prior to use.
(2) Preliminary mounting requires two steps, one step of axially pressing the bolt to move the slat below the channel flanges of the channel rail, and the other step of rotating the bolt by 90 degrees to swing the slat in a direction perpendicular to the channel rail. These operations are cumbersome. Also, an operator is subject to fatigue since his wrists are repeatedly twisted.
(3) Preliminary mounting requires a screwing operation. If the bolt is inadvertently rotated in a counterclockwise direction, the slat is disengaged from the bolt and may drop in the channel rail. Removal of the bolt requires substantial effort and time and thus deteriorates efficiency. Also, where the channel rail has a downwardly directed opening, the operator is subject to injury if the slat and articles are disengaged from the bolt and the fixture body and hit the operator's head and face.
(4) Rotation of the slat is limited when the longitudinal front end of the slat is contacted with the inner walls of the flanges. The slat may not be oriented at right angles to or may be obliquely engaged with the channel rail, depending on the configuration of the inner flange walls. This retards rotation of the bolt and causes the slat to be raised in an oblique fashion. If this occurs, the slat can not firmly be secured to the channel rail since a sufficient clamping area between the end surfaces of the downwardly directed rail walls and the slat is not available.
To this end, the inventors of the present application proposed a fixture for securing cable tubes as disclosed in EP 0553 765 A1.
The prior art fixture comprises a fixture body, a bolt extending through the fixture body, and a clamp threadedly engaged with the bolt. The clamp includes a central nut, and a pair of right and left clamping elements pivotably mounted to the nut and pivotable about a horizontal axis. Each clamping element has a clamping surface engageable with the lower surfaces of channel flanges, and stop surfaces extending upwardly from the clamping surface and contacted between the channel flanges. A spring is disposed between the head of the bolt and the fixture body to lift the clamp and the bolt. The fixture body has opposite side walls adapted to clamp the stop surfaces of the right and left clamping elements to hold the clamp relative to the fixture body.
In the prior art, electric line parts can be preliminarily mounted by axially pushing the bolt.
A problem with the prior art is that since the bolt constantly extends upwardly from the fixture body, external force may cause inadvertent operation of the clamp. Another problem is that the clamp is susceptible to displacement if the side walls of the fixture body are not equal to the distance between the stopper surfaces of the clamping elements. As to the latter problem, a clamping force is barely created if a space is left between the opposite side walls and the stop surfaces. In such a case, the clamp is likely to be displaced prior to use. If the bolt is pushed while the clamp is displaced, the clamp is inserted in an oblique fashion into the opening of the channel rail. On the other hand, an excess amount of clamping force is created when the distance between the opposite side walls is too short. If this occurs, assemblage becomes cumbersome. Also, the clamp may not be lowered even if the bolt is strongly pushed.
In the prior art, the stop surfaces of the clamping elements are snugly fit within the channel flanges of the channel rail. This arrangement insures lifting of the clamp and prevents rotation of the clamp about a vertical axis during a clamping operation.
The distance between the channel flanges of the channel rail to be secured has effect on vertical upward motion of the clamp and rotation of the clamp about a vertical axis. A problem also arises when the height of the channel flanges differ from each other, or when the clamp is not appropriately positioned relative to the bolt even if the channel opening has a required width. In other words, the stop surfaces are undesirably moved below the lower ends of the channel flanges to cause pivotal motion of the clamp about a vertical axis during a clamping operation. This makes it difficult to orient the clamp at right angles to the channel flanges. To this end, it is conventionally necessary to prepare various types of clamps to accommodate various types and sizes of channel rails to be secured. Also, it is necessary to carefully mount the clamp to the bolt during assembly of the fixture.